Powdery mildew is a common fungal disease of numerous ornamental plants (including dogwood, rose, phlox, and many bedding plants) that is commonly observed when atmospheric conditions provide warm days and cool nights. While powdery mildew does not always cause serious damage to an infected plant, it is capable of interfering with normal growth and reproduction. If the fungal infestation is severe enough, significant plant decline can be observed.
The powdery mildew fungus grows over the surface of tender leaf and stem tissues. The hyphae and conidia of the fungus cause the leaf to take on a white to gray appearance. Youngest leaves are typically infected first. Haustoria penetrate the leaf epidermal cells and act as anchors for the fungus. The haustoria also provide the fungus with water and nutrients taken from the plant. As a result of infection, the plant slowly declines. Dwarfing, distortion, chlorosis, premature senescence and browning of leaves, and blemished or aborted fruits and flowers are other manifestations of the fungal infestation. Infected plants will often produce new growth; infestation of this new growth with powdery mildew is governed by environmental conditions.
Chemical control is seldom recommended in the home landscape, however commercial operations depend upon chemical control in order to maintain salable plant materials. When chemical control is necessary, fungicides such as chlorothalonil (Daconil 2787), triadimefon (Fung-Away, Bayleton), propiconazole (Immunex), and triforine (Funginex, Triforine) are used. Fungicides protect healthy tissue from infection, however these same fungicides are incapable of curing infected tissue. Aside from the inability of the fungicides to kill powdery mildew, there are significant costs associated the use of fungicides in the control of this plant parasite. Typical fungicides used in the control of powdery mildew have costs in the hundreds of dollars per quart of fungicide. On a commercial scale, the nurseryman bears significant monetary costs to ensure that a salable material is maintained for consumption by the consumer.
Dogwoods have been particularly hard hit by powdery mildew. In Tennessee, a state that is known for its dogwoods, dogwoods are worth some $40 million to the state""s economy each year. Dogwood anthracnose has wiped out dogwoods in Tennessee and all across the eastern United States. Unfortunately, publicity about dogwood problems have caused sales to plummet, even in areas of the country that have not been affected by dogwood anthracnose. The disease, which thrives in damp shady areas, has not only decimated dogwoods in some landscapes, it has also made a major dent in the nursery industry. The cost of producing dogwoods has gone up dramatically because of fungicide use. Producing dogwoods has become very expensive which, in the long run, means that the cost to consumers is increased.
In addition to being expensive, chemical control of powdery mildew is also undesirable from environmental and health perspectives. The active ingredients in many of the fungicides used in the control of this plant parasite are known carcinogens. Further, prolonged contact of these fungicides with the skin of the person applying the chemicals to the plant materials is known to be harmful. In some cases, allergic reactions are known to result. Many of these chemicals are also harmful to aquatic life and care must be exercised to prevent accidental contamination of soil and/or groundwater. Accordingly, it is of great interest to the industry to identify alternative means by which to confer resistance to infestation with powdery mildew.
The subject invention provides plants with excellent resistance to powdery mildew. In a specific embodiment, the subject invention provides dogwood (Cornus florida) cultivars that are resistant to infestation with powdery mildew. Specifically exemplified herein are cultivars identified as xe2x80x98Jean""s Appalachian Snowxe2x80x99, xe2x80x98Kay""s Appalachian Mistxe2x80x99, and xe2x80x98Karen""s Appalachian Blushxe2x80x99.
The present invention also provides materials and methods for identifying, characterizing, and/or producing powdery mildew resistant plants. In a specific embodiment, the subject invention provides polynucleotide sequences, and patterns of polynucleotide sequences, which are associated with resistance to powdery mildew. These polynucleotides are characteristic of the powdery mildew resistant plants as described herein. Such polynucleotides are particularly useful in identifying and characterizing plant having resistance to powdery mildew.
The polynucleotide sequences disclosed herein are useful in methods including, but not limited to, enhancing plant resistance to powdery mildew. The disclosed polynucleotide sequences are also useful in the identification of similar polynucleotide sequences in other varieties of powdery mildew resistant plants. The subject invention further pertains to the use of the disclosed polynucleotide sequences, or fragments thereof, in assays to characterize and/or identify genes associated with resistance to powdery mildew. Also contemplated according to the subject invention is the use of oligomers from these polynucleotide sequences in kits that can be used to identify genes that confer powdery mildew resistance.
Other aspects of the invention include use of polynucleotide sequences to produce purified polypeptides. Still further aspects of the invention use these purified polypeptides to produce antibodies or other molecules able to bind to the polypeptides. These antibodies or binding agents can then be used, for example, to analyze cells in order to localize the cellular distribution of polypeptides. The antibodies are also useful for the affinity purification of recombinantly produced polypeptides.